Optical communication systems are a substantial and fast-growing constituent of communication networks because of their large transmission bandwidth and low signal losses. Currently, the majority of optical communication systems are point-to-point networks configured to carry optical signals over one or more optical waveguides from a transmit terminal to a receive terminal. The use of optical communication systems has also expanded into local network architectures, such as local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs).
Currently, communications networks employ optical fiber as the transmission medium and electronic devices for processing of the received signals. In this type of network, switching is performed by electronic components where the optical signals transmitted over a fiber are first converted to their electronic equivalent and subsequently processed. However, electronic switches are better suited for use at transmission data rates lower than the current state of the art. This necessitates electronically demultiplexing the signals, performing the switching, then multiplexing the signals up to the transmission rate. A drawback associated with these switching systems is the introduction of unwanted processing delays into the network caused by converting signals from optical to electrical and back to optical form. Thus, the speed advantage associated with optical signal transmission is compromised. Moreover, these electronic switches have to be adapted for a given data rate and format within a communications network. With the increasing signal bit rates, for example 10 Gbps, electrical connections between the individual switching elements is difficult and an optical solution is preferred. In a WDM environment optical switches offer the advantage that they can switch a multiple of transmit signals simultaneously without requiring optical demultiplexing as required for single channel electronic switching.
Optical switches are transparent in that they allow signal transmission independent of data rate and format. Consequently, optical switching components as well as high speed electronic cross point switches are being developed to accommodate increasing complexity associated with large optical communications networks.
Large optical or electronic switches can be constructed from smaller switching elements with the number of input and output ports ranging from, for example, 2 to 32. One approach to build these large switches from small switching elements is the Clos Architecture. The basics of this type of switch are discussed in "A Study of Non-Blocking Switching Networks" by Charles Clos, The Bell System Technical Journal, March 1953, pp. 406-424. This type of switch requires at least three stages to provide connections from an input to a particular output from among all the possible connections within the switch which is referred to as "non-blocking." FIG. 1 is a block diagram of a portion of a switch 10 using the Clos Architecture. The input stage 15 includes K.times.N switching elements 20.sub.1 . . . 20.sub.M, the next stage 30 includes M.times.L switching elements 35.sub.1 . . . 35.sub.N, where M and N are integers. Accordingly, the number of connections (electrical or optical) needed to interconnect stages 15 and 30 is given by M.times.N. By way of example, where M=64 and N=64, 4096 connections are needed to connect the two stages in a non-blocking configuration. The switching elements 20.sub.1 . . . 20 .sub.M, 35.sub.1 . . . 35.sub.N may be electrical or optical. Such optical s witching elements include directional couplers, digital optical switches, opto-mechanical switches, etc. When optical elements are employed, the switching process and transmission of signals between the switching stages are in optical form. Stages 15 and 30 can also include electrical switching elements with optical interconnection by means of transmitters and receivers at the respective inputs and outputs of each stage. This configuration may be useful, for example, when the various stages of a switch are physically separated, thereby making electrical transmission between stages less advantageous.
In the simplified example illustrated in FIG. 1, each input stage switching element 20.sub.1 . . . 20.sub.M has K=5 inputs and N=2 outputs. Each stage 30 switching element 35.sub.1 . . . 35.sub.N has M=4 inputs and L=8 outputs.
Currently, the manufacturing process for the fiber interconnection pattern 25 between switching stages is performed either manually or by robot arms. In each of these cases, individual fibers are connected from output ports of switching elements 20.sub.1 . . . 20.sub.M to input ports of switching elements 35.sub.1 . . . 35.sub.N. As described above, with the increasing complexity of these switches, the number of connections can run into the thousands and tens of thousands. This presents a large number of individual fibers to manage. This can cause problems when attempting to trace a particular connection, for example, when a fault or break occurs, or merely trying to keep track of input/output connections when forming such a non-blocking switch configuration. Moreover, optical fiber is bend sensitive. This can cause problems when installing and handling the high number of fibers when forming the interconnects.
Thus, there is a need to provide an apparatus and method which simplifies the process of forming optical fiber interconnects between switch stages.